首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   477274篇
  免费   4482篇
  国内免费   1541篇
电工技术   8113篇
综合类   606篇
化学工业   72589篇
金属工艺   23365篇
机械仪表   16381篇
建筑科学   10064篇
矿业工程   4619篇
能源动力   10107篇
轻工业   30258篇
水利工程   6488篇
石油天然气   16022篇
武器工业   68篇
无线电   49234篇
一般工业技术   106162篇
冶金工业   76209篇
原子能技术   15616篇
自动化技术   37396篇
  2021年   4425篇
  2019年   4251篇
  2018年   7859篇
  2017年   8184篇
  2016年   8685篇
  2015年   4988篇
  2014年   8563篇
  2013年   20159篇
  2012年   12904篇
  2011年   16964篇
  2010年   13472篇
  2009年   15299篇
  2008年   15680篇
  2007年   15399篇
  2006年   12935篇
  2005年   11730篇
  2004年   11589篇
  2003年   11289篇
  2002年   10924篇
  2001年   10836篇
  2000年   10443篇
  1999年   10192篇
  1998年   22066篇
  1997年   16288篇
  1996年   12471篇
  1995年   9814篇
  1994年   8820篇
  1993年   8969篇
  1992年   6978篇
  1991年   6913篇
  1990年   6823篇
  1989年   6713篇
  1988年   6346篇
  1987年   5926篇
  1986年   5846篇
  1985年   6358篇
  1984年   5977篇
  1983年   5683篇
  1982年   5281篇
  1981年   5432篇
  1980年   5407篇
  1979年   5367篇
  1978年   5559篇
  1977年   5881篇
  1976年   7178篇
  1975年   4918篇
  1974年   4981篇
  1973年   5020篇
  1972年   4353篇
  1971年   3945篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
941.
In order to relax alignment tolerances on single-mode fiber interconnection, we propose an end face treatment to realize an expanded mode fiber. This new technique consists of splicing fibers with various lengths and characteristics. The spot size and coupling properties are analyzed numerically considering the effects of gap, offset, and tilt. Low loss, wide misalignment tolerances, and low cost are achieved. The fabrication process and experiment results are presented. The performance of a connector with this expanded fiber is reported.  相似文献   
942.
We demonstrate for the first time a high-power P-i-N diode with local lifetime control using the proximity gettering of platinum in the FZ silicon. The region of maximal damage resulting from the low-dose helium implantation was decorated by substitutional platinum that diffused from the PtSi anode contact at low temperature (700°C) through the P+-P anode doping at the distance of 70 μm. The diodes show very low forward voltage drop with negative temperature coefficient and very low leakage current even at elevated temperatures while keeping the major advantages of the ion irradiated devices like low turn-off losses and soft recovery  相似文献   
943.
944.
945.
The major risk factors and processing steps that can lead to contamination of green coffee with ochratoxin A (OTA) have been identified. Surveys of the green coffee production chain indicate that Aspergillus ochraceus and A. carbonarius are the most potent OTA producers on coffee. Both have been successfully grown in vitro on green coffee and coffee cherries, respectively, producing high amounts of OTA (5-13 mg kg -1 ). The so-called dry processing of coffee, which is cherry drying, was identified as one of the steps during which OTA formation can take place, particularly under humid tropical conditions. Cherries contain sufficient amounts of water to support mould growth and OTA formation during the initial 3-5 days of drying on the outer part of the cherries. Not surprisingly, after dehulling, husks can be highly contaminated with OTA, as also indicated by its enhanced concentration in soluble coffees adulterated with husks and parchment. A minimum water activity of 0.80 (about 14% MC) is required for in vitro OTA production on green coffee, a fact that does not rule out the possibility of OTA contamination due to improper transportation and storage of green coffee. However, this appears not to be a major route for OTA contamination of coffee. OTA contamination can clearly be minimized by following good agricultural practice and a subsequent post-harvest handling consisting of appropriate techniques for drying, grading, transportation and storage of green coffee; these procedures are well established.  相似文献   
946.
947.
The evolution of investigations into glass properties is described with the use of the SciGlass information system on the basis of an analysis of the world literature on glass from the end of the 19th century to the present day. Variations in the total amount of published data, in the interest of researchers in certain glass components and their properties, in the specific features of forming research groups, and in the general quality of publications are considered. Measures are proposed that can prevent a further decline in the quality of published experimental results.  相似文献   
948.
As the wave of globalization washes over geographical boundaries, the world steps into the era of a new knowledge-based economy with governments striving to encourage innovation in industry especially through national systems of innovation. A national system of innovation (NSI) is considered important because how a nation utilizes and exploits its NSI will determine whether it can compete and ride the wave of globalization or be carried by it and thrashed onto the shores of the new economy. This paper seeks to highlight the linkages developed for enabling communication among the various NSI stakeholders for achieving goals in one such effort, viz. the Multimedia Super Corridor (MSC) Cluster of Malaysia. The MSC offers a vision to create a global multimedia climate through an integrated environment of interlinked elements and attributes. The government of Malaysia, realising the significance of the NSI as a way to better utilize, exploit, and enhance systems, is making efforts to this effect. The efforts include bringing together various stakeholder organizations under the "Multimedia Flagship Applications" to develop flagship applications. This is for the development of information technology applications to pave the way toward a knowledge-based economy. The MSC Cluster is presented here as a physical manifestation of the NSI, and it gives an idea as to how policy makers can design linkages for communication among the various stakeholders to further national innovative performance and competitiveness in general.  相似文献   
949.
950.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号